Merge lane base check: develop e391369849e7

Merge lane base check: run the full gate on `develop` at `e391369849e7f1a157a227db8a66488eb6f05619` alone and report it certified or red: nothing had certified it since the last attempt. A red verdict files a fix task; it never holds the lane. Filed by the control plane (`app/merge_lane.py::_certify_idle`). How: run `python3 tools/merge_lane.py run` once. It takes this check's batch, gates that commit with the full gate in its sandbox and reports `certified` or `develop_red` itself. Never run the gate by hand: a hand-run green reports nothing, so no certificate is recorded.

develop e391369 reported develop_red. Both full-gate runs failed on sandbox DNS timeouts reaching image registries (lychee pull, then cgr.dev during compose build), not on the code: 9118 tests passed, 0 failed. Memory: proposed mem-29102.